


XX, X?, XY

by Geist



Category: Homestuck, MS Paint Adventures
Genre: Anal, Anal Sex, Blow Jobs, Crossdressing, Cunnilingus, F/M, Futanari, Hermaphrodites, Heterosexual Sex, M/M, Male Homosexuality, Oral Sex, Other, Pegging, Rough Sex, Rule 63, Sex, Sexual Content, Strap-Ons, Transformation, Vaginal Sex, Yaoi
Language: English
Status: Completed
Published: 2012-06-25
Updated: 2012-06-25
Packaged: 2017-11-08 13:13:28
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 19,028
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/443554
Author URL: https://archiveofourown.org/users/Geist/pseuds/Geist
Summary: <blockquote class="userstuff">
              <p>Karkat 'rests his eyes' for a few seconds. When he wakes up an hour later, he's not the same gender he started as. Three chapters, three different endings!</p>
            </blockquote>





	1. XX

Some time ago, Karkat had sat down in his room and closed his eyes, purely for the purposes of resting them, certainly not to sleep and be cast into one of those terrifying Gods-spun dream bubbles. When he'd opened them an hour later, he'd stood up and found himself feeling...different. A quick glance in a mirror told him what had happened.

His features had softened, his hips had grown and his stomach had become slightly more slender. He was definitely shorter. Even his hair had lengthened. To top it all off, his chest now bore a pair of breasts that were inadequately constrained by his male-design t-shirt. More privately, his pants felt tight around his widened hips, but loose and empty elsewhere. Dreading what he might see, he unbuckled them, slid them down a little way, then pulled his boxer shorts down after them.

He stared in shock. There was no denying it. He was now a she.

Something in the Veil had changed Karkat, and she had a fairly good idea of what or who it might be. She pulled up her shorts and pants, strode into the transportalizer out of her room and stalked through the corridors of the asteroid lab, a once moderately angry boy who was now a steamingly furious girl. Her target was going to rue fucking around with her like this.

***

Eridan Ampora did a little twirl in front of the mirror, smiling as his pleated tartan skirt clung flatteringly to his legs. Black and purple striped stockings and a tight tank-top bearing his symbol completed the ensemble. His hair had been washed clean of its usual styling product, no mean feat given that it was almost entirely waterproof. His locks now hung in a pair of loose bunches. A dab of tyrian purple lipstick made for a final elegant touch.

Eridan could feel his cock hardening. It always did when he looked at himself like this. It wasn't his fault. He just made such a damn attractive girl. He smiled at his reflection, watched it smile back.

His stiffening member was starting to poke out over the waistband of the too-tight lace panties hidden beneath his skirt. It began to tent the folds of the skirt, making it very obvious what kind of a state he was in. So it was understandable that he panicked slightly when he heard the transportalizer to his chambers charging up and teleporting someone in.

Eridan desperately reached up and wrenched at his top, but before he could get anywhere close to changed, Karkat walked in and began to harangue him.

“ERIDAN,” she screamed. “YOU STUPID FUCKASS! IF YOU'RE GOING TO PRACTICE THAT STUPID WHITE SCIENCE SHIT DON'T GET ANY OF IT FUCKING NEAR ME!”

“Huh, me?” Eridan replied, temporarily distracted by Karkat's rage. “I haven't fuckin' done anything, Kar.”

“OH YEAH!? THEN WHY IN THE NAME OF THE CONDESCE'S RANCID FISHY NOOK AM I A FUCKING...wait, what?”

Karkat broke off, and stared at Eridan. Eridan stared back and realised what was different about his team leader.

“What the...” he began.

“...fuck?” Karkat concluded.

“Why are you...”

“No, why are YOU dressed as a girl?” Karkat said before Eridan could finish his question. It made no difference, as Eridan simply riposted:

“Why ARE you a girl?” He smirked. “Nice jugs, by the way.”

Karkat glared wordlessly at him for a moment. Then she stepped forward, belted him hard across the jaw and while he was stunned, grabbed him by the neck and pinned him against the wall.

“You did this to me”, she said.

“I didn't,” Eridan rasped.

“You did. You and that gogdamn wand of yours.”

“I swear Kar, I fuckin' didn't. It must have been some sort of natural effect. But...I think I can turn you back.”

Karkat glared at him for a moment more, then took her hand away. Eridan gasped for breath and reached up to his bruised throat, rubbing it for a second before grinning foolishly at her.

“You've got a good grip for a girl,” he said. “So what do I call you now? Karkatte? Kattie?”

“Stick with Kar if you don't want to swallow your teeth,” Karkat said, cracking her knuckles.

“Okay, okay, whatever.”

They went quiet for a moment, then Karkat said, “Well?”

“Well what?”

“Well are you going to turn me male again, idiot?”

“Mmmm...no.”

“WHAT!?” Karkat roared, stepping forward again. But Eridan defended himself this time, taking her wrists in his hand and holding her vengeful fists away from his face.

“I'll turn you back, Kar, but you gotta do something for me first.” He grinned creepily.

A sudden flash of fear filled Karkat. She shook her hands out of his grip and took a step back. “Oh no...no way.”

“No way?” Eridan's smile grew wider.

“No way am I letting you fuck me, you freak! It wouldn't have happened when I was male and it's not happening now!”

Eridan widened his eyes in mock surprise. “Why Karkat,” he said, “who said anything about me fuckin' you?”

He turned and crossed the room, riffling through a cabinet set against one wall. He returned, carrying something and saying, “I want you to fuck ME.”

Karkat stared at the contraption Eridan held. It was an assembly of black straps and metal buckles, surmounted by a long, thick, rubbery dong. “That's a...” she said.

“Strap-on, yes.”

“And you just happen to have it lying around.”

Eridan nodded. “Yup.”

“In case someone came along to fuck you with it?”

“Mmhmm.” He seemed entirely unembarrassed about revealing this desire. “Was hoping it was gonna be Fef, you know, but you'll do.”

“Yeah, it's still not happening.”

“You do want to be a boy again, don't you?” Eridan teased. “You can either wait until this wears off, which might be never, or we can have one quick fuck, after which I'll zap you with the awesome power of my white science and we'll both be happy. Well, I'll be happy. Don't know about you.”

Karkat thought, unable to believe that she was even considering it. The idea of even getting close to Eridan was disgusting. But she really had no choice. She couldn't let Terezi or Vriska see her like this. Their laughter would probably burst her eardrums. Eventually she said, “One quick fuck.”

“Unless you want more.”

“Ugh, Gog no.”

“Whatever. Are we doing this?”

“Fine, you win,” Karkat groaned.

“Alright. Strip.”

“What? No!” Karkat grimaced in revulsion.

“Full nudity, or this goes nowhere. My science, my rules.”

“Can't I just put the thing on over my pants?” she asked desperately.

“Nope.”

“You're the worst kind of fucking creep, Eridan.”

“Yeah, but I'm the one with the wand. And I bet you want your wand back, huh?”

Karkat heaved an appalled sigh and pulled her shirt off, freeing her magnificent new tits. Eridan leered. “Niiiice,” he drawled. “You make a pretty hot girl, Kar. Pity you're an ugly guy.”

“Fuck you.”

“You will. Now your pants.”

Karkat hadn't thought much about exposing her boobs. It wasn't much different from going bare-chested as a male, even if Eridan was getting his sick little thrill out of it. But that demand gave her pause for thought. If she took off her pants, she'd only be a pair of boxer shorts away from being completely naked. Reluctantly, she squatted down and took off her shoes and socks, then stood up, popped the fastener of her pants and gripped the waistband. She slowly wriggled them down over her hips, then down to her ankles, where she stepped out of them. Eridan watched with a lascivious glint in his eye. “Now,” he said huskily, his voice almost catching, “your shorts.”

Desperately trying not to blush, Karkat slid off her underpants. When her privates were exposed, she covered them with her outstretched palm, using her other hand to help pull her boxers all the way off. She straightened up and stared defiantly at Eridan.

He tapped his foot impatiently. “Show me,” he said.

Karkat made a face and took her hand away from her crotch, letting Eridan's greedy gaze fall on her delicate, virgin folds. Eridan could feel his cock pulsing harder the longer he looked. He wondered whether he should be the one penetrating, imagining Karkat's warm, unwilling vagina wrapped tight around his prick. He decided against it. Karkat would probably be far from amenable. Besides, he was fulfilling a fantasy here.

“Getting a good look, perv?” Karkat said. Eridan realised he'd been staring at her snatch for a little too long. In lieu of a response, he tossed her the strap-on. She just about caught it, suppressing her distaste for it long enough to hook her fingers around one of the straps.

“Put it on,” Eridan demanded.

Karkat did so, stepping into it and drawing the harness up to her thighs. It fastened snugly around her hips and arse. To her relief, it covered her crotch. Calling it clothing was a bit of a stretch, but at least she wasn't completely naked now.

Eridan nodded approvingly, then went back over to the cabinet from which he'd taken the strap-on. He reached in, grabbed a bottle of lube and brought it back to Karkat. “Oil it up, Kar,” he said.

With a growl, Karkat opened and upended the bottle, squeezed a tiny amount of lube over her prosthetic cock and gave it a cursory rub. Eridan noticed, and gestured for her to put more on. “Nice and thick,” he said, leering. “Do it like you were jacking off your own bulge.”

“You stupid fuckhead,” Karkat said, but she complied. She drizzled the dong in lube and pistoned her clenched hand up and down its length.

Smiling, Eridan imagined the glistening plastic prick filling him. His cock responded to his thoughts, straining hard against the confines of his panties. He reached beneath his skirt and loosened them, letting them drop. He daintily pulled one foot free, keeping them wrapped around the other. He sat down and lay back. His skirt fell back with him; his cock sprang free, standing out proudly from his crotch. He clutched his buttocks and spread them wide apart. Breathing heavily he said, “Alright Kar. Fuck me!”

“Oh, my pleasure,” Karkat snarled. She dropped to her knees and shuffled forwards. She grabbed one of Eridan's ankles and pushed it back, further exposing what Karkat had to admit was a rather nice tight arse. She guided the tip of the slippery dildo to the entrance of Eridan's hole.

“A-ah, careful, Kar,” Eridan said. He could feel the cool plastic pressing against his ring. With Karkat looming over him, he didn't feel as though he was in as much control of the situation as before. He almost gulped as his whimpering caused Karkat's mouth to twist in a sadistic grin.

“What's the matter, Eridan?” she said. “Reality not living up to the fantasy?”

“No. Actually, maybe, if all you're going to do is fuckin' talk.”

Without any warning, Karkat thrust her hips forward, forcing the head of the strap-on into Eridan's arsehole. He yelped, sudden pain flooding him.

“Hey, fuckin' gently, you stupid nooksucker!”

“Ready for the rest?” Karkat said, almost sweetly.

“Wait, fuck nAAAAGGGGH!”

Karkat slammed the rest of the strap-on home, reaming out Eridan far faster than was comfortable. His screams filled the room. He clenched his hands into tight fists, nails digging into his palms. Tears pooled in his eyes, then overflowed and made black mascara trails roll down his cheeks. His chest felt like it was going to burst as his need to breathe and his desire to scream warred with each other, until at last he was able to take a shuddering gulp of air. That was enough to give him a semblance of control over his body. He feebly tried to throw Karkat off, but every move he made just brought more pain, so in the end he just lay still and waited for it to be over.

When the pain had subsided from unbearable to merely feeling like his arse was on fire, Eridan blinked the tears out of his eyes and said, in between sniffles and sobs, “Don't you ever – ahuh – don't ever do that again.”

“Trust me,” Karkat said sourly, “I won't give myself the opportunity.” Then she smiled and purred, “Besides, I thought this was what you wanted?”

“Not like this, you fuckin' -” His insult was cut short as Karkat reached out and slapped him hard. He clutched at his cheek and gaped at her. “You dare-”

She slapped him again. “Yeah I dare. Because I know you love it, don't you?” Another slap. Eridan whined. “And you know, I'm beginning to enjoy it a little too.” That was true enough. The feeling of dominance fizzled in her blood, all the old trollish instincts coming to the fore. They screamed their demands to take, to use, to control. Karkat looked down at Eridan's tear and make-up streaked face, at the purple bruises forming where her palm had met his skin, and at the impotent anger in his expression. “You know,” she said, “you're looking pretty pitiable right now.”

Eridan choked down his shock at those words. He couldn't ever have imagined Karkat of all people becoming matesprits with him. Besides, he couldn't possibly reciprocate. Right now she was anything other than an object of pity. She was terrifying.

“Just...do what you're going to do,” he muttered.

Karkat gave no response, but pulled back. The strap-on slowly slipped out. Eridan felt more twinges of pain in the tissues of his abused rectum, but they were mere prickles compared to the agony of before. Karkat pulled out most of the dildo, leaving just the head lodged inside. She grabbed Eridan's legs and practically folded him back on himself. He felt his cock pressing into his stomach. To his amazement, it was still hard, and had even developed a little bead of purple-tinted pre-cum at the very tip.

Karkat either didn't notice or didn't care about Eridan's dick. Probably a combination of both, Eridan reasoned, as she seemed far more intent on flipping the humiliation tables on him as fast as possible. She thrust back in, slower than when she'd first entered him, but still fast enough to make him groan as his arse struggled to accommodate the dong's bulk. She bottomed out, held herself there for a moment, then repeated the cycle. Eridan found it easier to take this time, and behind the pain was something that might be called pleasure.

As Karkat built her momentum, she found that her new body could feel good too. When she forced the strap-on into Eridan's arsehole, she felt it push back against her pussy, the leather of the harness rubbing against her clitoris. She sensed a growing need within herself. It was like having a hard-on, but more...inverted? She wasn't sure how to describe it. Everything felt new and yet familiar at the same time.

And then there was the wetness. Karkat knew perfectly well what was going on, but it was still weird to experience it. Her vagina drooled a steady stream of juice, turning the inside of the harness into a swampy mess that slid deliciously against her folds. Pounding Eridan's arse made her moisture leak out around the edges, carving little runnels down her thighs and dribbling out onto Eridan's buttocks.

Morseo than in her male form, Karkat was aware of her nipples. Maybe it was because they came as part and parcel of the most noticeable changes to her anatomy, or maybe it was because they were just so much bigger and more sensitive than before. Either way, both of the pert nubs stuck out in startling erection, begging for attention almost as vocally as her pussy. 

Karkat let go of one of Eridan's legs – he gratefully let it relax and rest on her shoulder – and brought her hand up to her breasts, squeezing the tender flesh. She flicked an experimental fingertip across one of her nipples and found it produced a burst of pleasure that made her gasp out loud. She played with her tits, focussing on their stiff little summits as much as she possibly could. Her eyes closed as for the first time she truly enjoyed her femininity.

Eridan was beginning to enjoy himself too, now that his arse had become accustomed to the strap-on. Karkat was still giving him a violent fucking, but there was a bit less anger behind it now. He found pleasure in the feeling of tight fullness when Karkat's hips pressed against his butt and forced the dildo into him, sighed as it left and brought both relief from the stretching and a sense of emptiness, then gasped as it reamed him out again. The constant sliding of hard plastic over sensitive nerves produced a continuous buzz, and every so often a nova of almost unbearable pleasure would flare within him as Karkat angled the dildo just right to bump against his prostate. It was all he could do to keep himself from moaning out loud when that happened, but he made the effort. He feared Karkat's scorn, though he didn't really know why.

With all of Eridan's attention focussed on his arsehole, his cock went unattended to. Soon though, it became impossible to ignore. It was a hot, pulsing, solid rock of an organ. His balls felt swollen. They drew down great loads of fluid from his genebladder, ready for the first volley of his climax; subsequently, his cockhead leaked pre-cum, a purple stain spreading out across his dishevelled skirt.

Eridan took hold of his cock and began to run his hand up and down its length, spreading his sticky-slippery pre out along his shaft. It felt incredible; having his prick and his arse stimulated at the same time produced sensations beyond compare to any other debauchery in which he'd indulged. He clapped his hand to his mouth, trying to muffle the little moan of “Oh...oh fuck,” that escaped him. He wasn't going to add to his humiliation if he could help it.

Karkat could hardly fail to notice his hands moving to opposite ends of his body, though, and she gave Eridan a smirk that set his teeth on edge. She took his squeaks as a sign to pound his butt even harder, perhaps trying to spoil his pleasure with a little more pain. It had the opposite effect: the extra speed was just what he needed. He wailed in ecstasy and bucked his hips as best he could against her force. Now the strap-on hit his sweet spot with almost every thrust.

Eridan's hand flopped limply from his mouth as he opened it in a raucous scream. Conversely, the hand he had around his cock gripped it hard as it spouted gout after gout of hot purple seed across his stomach, his chest and, in one particularly vigorous spurt, his face. He shuddered bodily, the contractions of his balls sending surges of sexual delight through him. His prostate, still mercilessly battered by Karkat's unceasing thrusts, felt like a node of pure pleasure, and his arse pulsed around the strap-on as though trying to draw it even deeper within.

Karkat looked down triumphantly as her victim writhed in climax. As his orgasm subsided, she gave Eridan a few more desultory thrusts and said, “Enjoy that, freak?” Eridan could only moan weakly and nod in response.

Karkat pulled her strap-on from Eridan's arse, a little trickle of well-used lube dribbling from his distended hole after it. She sat back and watched Eridan recover, wondering what her next move should be.

Eventually, Eridan sat up and arranged himself into as dignified a pose as he could manage. He grinned and said, “Gotta admit, Kar, you started a bit rougher than I liked, but that was pretty fuckin' good.”

“Yeah, yeah,” Karkat said. It was a magical adventure for everyone. Now you're going to turn me back into a male and we're all going to forget that this happened.”

“Are we?”

“Yes,” said Karkat, with vehemence.

“Well I could do that,” Eridan said, “Or I could give you some of the attention you clearly so desperately need.” He nodded in the general direction of her crotch.

Karkat looked down, and saw that her thighs were completely streaked in the moisture of her pussy. Even the leather of the strap-on was soaked in it. And now that it had been pointed out, her earlier arousal returned like a stick of dynamite glued to a boomerang. Her desire to be penetrated radiated out from her pussy through her whole body. She could feel her swollen cunt lips pressing hard against the strap-on, and felt her clit throbbing with every beat of her heart.

“I...fine,” she said. “But I'm only doing this for me. And I stay in control. On your back.”

Eridan smiled and lay back down. His cock was semi-rigid, wrapped in his skirt and still drained from its previous ordeal. It was rapidly regaining strength, though, and as Karkat peeled off the strap-on to reveal her dripping cunt, his prick surged back into full hardness.

Karkat straddled Eridan, one hand on his chest and the other on his cock. He moaned as her soft, slim fingers manipulated it into a comfortable position. She bit her lip as she hovered over it, his cockhead just brushing her labia. Even as a male she'd never experimented with being the penetratee, and now she was dealing with a totally unknown quantity. Her new organ seemed to be wet, relaxed and ready enough, however, and so with just the slightest gasp she impaled herself full length on Eridan's member.

Eridan's whole body went rigid as Karkat's silky-smooth walls enveloped his penis. It, on the other hand, seemed to melt, the heat of his arousal rushing out to mix with Karkat's. Then she began to move, and Eridan's eyes rolled back in his head even as he squeezed his eyelids shut in sheer bliss. Being fucked hard in the arse had been great, but there was nothing quite like having some hot little pail-filler ride his dick. He moaned, and wondered how someone who'd had a vagina for less than an hour was so good at using it.

Karkat's thoughts ran along similar lines. Her hips seemed to be guided almost instinctively into the positions that felt best for her. As she raised herself up and let gravity carry her back down, her clit bumped against Eridan's shaft, jolting her with pleasure. His cockhead poked hard into her sensitive insides, making her groan with pleasure and causing her walls to clamp down around his length. She put her hands on Eridan's chest for balance and began to bounce, slamming his prick into herself again and again. The rush of sensation made her dig her nails into his chest, and he hissed at the sudden pain.

Their mutual ecstasy quickly built as they fucked. Their emotions ran wild: pity mingled with hate until they forged something new and indistinguishable. Their every thought was modulated by the all-pervading demands of trollish hormones and pheromones. At times, their mating became more like fighting than sex. They clawed, pinched, slapped and bit each other. Eridan squeezed Karkat's tits until his nails pierced skin, bruised red crescents forming under his pitiless hands. She snarled in fury and raked her own nails across his face, gouging deep purple trails across his cheeks. Her other hand went to his balls and squeezed until he screamed and released her. Then, pain and exhaustion getting the better of them, they collapsed and became oddly tender, sharing kisses and running their hands over each other's bodies, massaging sore spots and cupping the swells of breasts and buttocks.

Their passions grew endlessly, until they were doing little more than pure, mindless fucking. Karkat's eyes were glazed as she hammered herself onto Eridan's shaft over and over. Little moans and squeaks escaped her as she fought her way towards orgasm. Eridan grunted and groaned every time she slapped against him, each thrust pushing him closer to the edge.

Karkat came first, throwing back her head and issuing a joyous scream. She slowed her thrusts and started to rise from Eridan's cock, but he grabbed her waist and forced her back down. Now his hips were the ones to buck from the floor. His teeth were gritted and his eyes were screwed tight shut as he desperately sought his own climax. At last it came, and his seed boiled up out of his balls as he uttered a guttural yell. Karkat, not wishing to fill a bucket, pulled up and away from him. His cock slipped out of her just in time, and she watched, slightly amazed, as his fluids fountained into the air. His orgasm wasn't quite as voluminous as before, but there was still plenty to refresh the drying purple stains across his body.

After a few seconds, it was done. Eridan's cock started drooping, and his and Karkat's gasps and heavy breathing faded into silence. Karkat sat lop-sided, her legs sprawled out to one side. Eridan waited until he felt sturdy enough, then hoisted his bruised, scratched, aching body up into a sitting position. He glanced at Karkat, but couldn't quite meet her eyes. She didn't seem able to either.

“So are we done, perv?” she mumbled.

“Yeah,” he replied. “Enjoy it?”

“Fucking...” There was a brief pause, then she continued, “yeah, I guess. You?”

“Oh yeah.”

Silence reigned again, then Eridan said “So, do you want me to...”

“Turn me back?” Karkat said, a little too eagerly. She stood up, grimacing, as she felt her loosened pussy dribble its warm fluids down her leg. Eridan followed her lead, then went off to find his wand.

Eridan returned with his wand, and pointed it with Karkat. She flinched a little. “It won't hurt,” he said scornfully. He cast his spell, and it was a simple one. A shimmering haze of energy enveloped Karkat and began to transform her, cell by cell, DNA strand by DNA strand. Her boobs were the first thing to go, shrinking into her chest until it was as flat as it had ever been. Her nipples shrank too, the areolae becoming smaller and much less puffy.

The magic started its work on her groin. She gasped and crossed her legs. Her vagina was sealing itself shut from the top down, and it was the weirdest sensation she'd ever experienced. She touched her hand to her crotch just in time to feel her labia and clit merge together, becoming smooth, bare skin. Nothing happened for a moment, then her skin began to bulge, splitting into three parts. She winced as her nerves plugged themselves into her new flesh. Her rapidly growing balls plumbed fresh channels back up to her genebladder. Her cock regained its former size and shape, down to the smallest capillaries and the most delicate folds of skin.

After that, just some minor adjustments to Karkat's body remained. Some parts thickened, others became thinner. The glow faded, Eridan lowered his wand and Karkat, to his immense relief, once again found himself fully and biologically male. He ran his hands up and down himself, checking that everything was in the right place. He caught Eridan looking and stopped, gruffly saying, “About time. Now where are my gogdamn clothes?”

Uncharacteristically, Eridan made himself useful and helped Karkat gather together his clothes. He handed them over and watched him dress in silence. When Karkat was done, he straightened up and said, “Right. Well...I'm going now. Sicko.”

“I ain't stopping you,” Eridan replied. “But feel free to come back.”

“Yeah right!” Karkat paused. “But if it does happen again, I'll need you to do what you just did.”

“What, all of it?”

“Just...shut up! It probably won't even happen again.”

Karkat stalked off to the transportalizer pad. Eridan, standing there in his cum-covered hair and clothes, his panties still around one ankle, watched him go. The transportalizer powered up and zapped Karkat away. Eridan smirked, and wondered if his white science could actually turn a boy into a girl. After all, it had worked perfectly well the other way around. Maybe he could try it out on himself some day.

Karkat stepped off the other end of the transportalizer and, despite himself, smiled. He wondered what had set the whole chain of events in motion. Perhaps it was something he ate? He walked off into the depths of the asteroid, vaguely looking for anything that seemed like it might have been responsible. Purely out of curiosity, of course.


	2. X?

Some time ago, Karkat had sat down in his room and closed his eyes, purely for the purposes of resting them, certainly not to sleep and be cast into one of those terrifying Gods-spun dream bubbles. When he'd opened them an hour later, he'd stood up and found himself feeling...different. A quick glance in a mirror told him what had happened.

His features had softened, his hips had grown and his stomach had become slightly more slender. He was definitely shorter. Even his hair had lengthened. To top it all off, his chest now bore a pair of breasts that were inadequately constrained by his male-design t-shirt. More privately, his pants felt tight around his widened hips, but loose and empty elsewhere. Dreading what he might see, he unbuckled them, slid them down a little way, then pulled his boxer shorts down after them.

He stared in shock. There was no denying it. He was now a she.

Something in the Veil had changed Karkat, and she had a fairly good idea of what or who it might be. She pulled up her shorts and pants, strode into the transportalizer out of her room and stalked through the corridors of the asteroid lab, a once moderately angry boy who was now a steamingly furious girl. Her target was going to rue fucking around with her like this.

***

Eridan Ampora did a little twirl in front of the mirror, smiling as his pleated tartan skirt clung flatteringly to his legs. Black and purple striped stockings and a tight tank-top bearing his symbol completed the ensemble. His hair had been washed clean of its usual styling product, no mean feat given that it was almost entirely waterproof. His locks now hung in a pair of loose bunches. A dab of tyrian purple lipstick made for a final elegant touch.

Eridan could feel his cock hardening. It always did when he looked at himself like this. It wasn't his fault. He just made such a damn attractive girl. He smiled at his reflection, watched it smile back.

His stiffening member was starting to poke out over the waistband of the too-tight lace panties hidden beneath his skirt. It began to tent the folds of the skirt, making it very obvious what kind of a state he was in. So it was understandable that he panicked slightly when he heard the transportalizer to his chambers charging up and teleporting someone in.

Eridan desperately reached up and wrenched at his top, but before he could get anywhere close to changed, Karkat walked in and began to harangue him.

“ERIDAN,” she screamed. “YOU STUPID FUCKASS! IF YOU'RE GOING TO PRACTICE THAT STUPID WHITE SCIENCE SHIT DON'T GET ANY OF IT FUCKING NEAR ME!”

“Huh, me?” Eridan replied, temporarily distracted by Karkat's rage. “I haven't fuckin' done anything, Kar.”

“OH YEAH!? THEN WHY IN THE NAME OF THE CONDESCE'S RANCID FISHY NOOK AM I A FUCKING...wait, what?”

Karkat broke off, and stared at Eridan. Eridan stared back and realised what was different about his team leader.

“What the...” he began.

“...fuck?” Karkat concluded.

“Why are you...”

“No, why are YOU dressed as a girl?” Karkat said before Eridan could finish his question. It made no difference, as Eridan simply riposted:

“Why ARE you a girl?” He smirked. “Nice jugs, by the way.”

Karkat glared wordlessly at him for a moment. Then she stepped forward, belted him hard across the jaw and while he was stunned, grabbed him by the neck and pinned him against the wall.

“You did this to me”, she said.

“I didn't,” Eridan rasped.

“You did. You and that gogdamn wand of yours.”

“I swear Kar, I fuckin' didn't. It must have been some sort of natural effect. But...I think I can turn you back.”

Karkat glared at him for a moment more, then took her hand away. Eridan gasped for breath and reached up to his bruised throat, rubbing it for a second before grinning foolishly at her.

“You've got a good grip for a girl,” he said. “So what do I call you now? Karkatte? Kattie?”

“Stick with Kar if you don't want to swallow your teeth,” Karkat said, cracking her knuckles.

“Okay, okay, whatever.”

They went quiet for a moment, then Karkat said, “Well?”

“Well what?”

“Well are you going to turn me male again, idiot?”

“Mmmm...no.”

“WHAT!?” Karkat roared, stepping forward again. But Eridan defended himself this time, taking her wrists in his hand and holding her vengeful fists away from his face.

“I'll turn you back, Kar, but you gotta do something for me first.” He grinned creepily.

A sudden flash of fear filled Karkat. She shook her hands out of his grip and took a step back. “Oh no...no way.”

“No way?” Eridan's smile grew wider.

“No way am I letting you fuck me, you freak! It wouldn't have happened when I was male and it's not happening now!”

Eridan widened his eyes in mock surprise. “Why Karkat,” he said, “who said anything about me fuckin' you?”

He turned and crossed the room, riffling through a cabinet set against one wall. He returned, carrying something and saying, “I want you to fuck ME.”

Karkat stared at the contraption Eridan held. It was an assembly of black straps and metal buckles, surmounted by a long, thick, rubbery dong. “That's a...” she said.

“Strap-on, yes.”

“And you just happen to have it lying around.”

Eridan nodded. “Yup.”

“In case someone came along to fuck you with it?”

“Mmhmm.” He seemed entirely unembarrassed about revealing this desire. “Was hoping it was gonna be Fef, you know, but you'll do.”

“Yeah, it's still not happening.”

“You do want to be a boy again, don't you?” Eridan teased. “You can either wait until this wears off, which might be never, or we can have one quick fuck, after which I'll zap you with the awesome power of my white science and we'll both be happy. Well, I'll be happy. Don't know about you.”

Karkat thought, unable to believe that she was even considering it. The idea of even getting close to Eridan was disgusting. But she really had no choice. She couldn't let Terezi or Vriska see her like this. Their laughter would probably burst her eardrums. Eventually she said, “One quick fuck.”

“Unless you want more.”

“Ugh, Gog no.”

“Whatever. Are we doing this?”

“Fine, you win,” Karkat groaned.

“Alright. Strip.”

“What? No!” Karkat grimaced in revulsion.

“Full nudity, or this goes nowhere. My science, my rules.”

“Can't I just put the thing on over my pants?” she asked desperately.

“Nope.”

“You're the worst kind of fucking creep, Eridan.”

“Yeah, but I'm the one with the wand. And I bet you want your wand back, huh?”

Karkat heaved an appalled sigh and pulled her shirt off, freeing her magnificent new tits. Eridan leered. “Niiiice,” he drawled. “You make a pretty hot girl, Kar. Pity you're an ugly guy.”

“Fuck you.”

“You will. Now your pants.”

Karkat hadn't thought much about exposing her boobs. It wasn't much different from going bare-chested as a male, even if Eridan was getting his sick little thrill out of it. But that demand gave her pause for thought. If she took off her pants, she'd only be a pair of boxer shorts away from being completely naked. Reluctantly, she squatted down and took off her shoes and socks, then stood up, popped the fastener of her pants and gripped the waistband. She slowly wriggled them down over her hips, then down to her ankles, where she stepped out of them. Eridan watched with a lascivious glint in his eye. “Now,” he said huskily, his voice almost catching, “your shorts.”

Desperately trying not to blush, Karkat slid off her underpants. When her privates were exposed, she covered them with her outstretched palm, using her other hand to help pull her boxers all the way off. She straightened up and stared defiantly at Eridan.

He tapped his foot impatiently. “Show me,” he said.

Karkat made a face and took her hand away from her crotch, letting Eridan's greedy gaze fall on her delicate, virgin folds. Eridan could feel his cock pulsing harder the longer he looked. He wondered whether he should be the one penetrating, imagining Karkat's warm, unwilling vagina wrapped tight around his prick. He decided against it. Karkat would probably be far from amenable. Besides, he was fulfilling a fantasy here.

“Getting a good look, perv?” Karkat said. Eridan realised he'd been staring at her snatch for a little too long. In lieu of a response, he tossed her the strap-on. She just about caught it, suppressing her distaste for it long enough to hook her fingers around one of the straps.

“Put it on,” Eridan demanded.

Karkat did so, stepping into it and drawing the harness up to her thighs. It fastened snugly around her hips and arse. To her relief, it covered her crotch. Calling it clothing was a bit of a stretch, but at least she wasn't completely naked now.

Eridan nodded approvingly, then went back over to the cabinet from which he'd taken the strap-on. He reached in, grabbed a bottle of lube and brought it back to Karkat. “Oil it up, Kar,” he said.

With a growl, Karkat opened and upended the bottle, squeezed a tiny amount of lube over her prosthetic cock and gave it a cursory rub. Eridan noticed, and gestured for her to put more on. “Nice and thick,” he said, leering. “Do it like you were jacking off your own bulge.”

“You stupid fuckhead,” Karkat said, but she complied. She drizzled the dong in lube and pistoned her clenched hand up and down its length.

Smiling, Eridan imagined the glistening plastic prick filling him. His cock responded to his thoughts, straining hard against the confines of his panties. He reached beneath his skirt and loosened them, letting them drop. He daintily pulled one foot free, keeping them wrapped around the other. He sat down and lay back. His skirt fell back with him; his cock sprang free, standing out proudly from his crotch. He clutched his buttocks and spread them wide apart. Breathing heavily he said, “Alright Kar. Fuck me!”

“Oh, my pleasure,” Karkat snarled. She dropped to her knees and shuffled forwards. She grabbed one of Eridan's ankles and pushed it back, further exposing what Karkat had to admit was a rather nice tight arse. She guided the tip of the slippery dildo to the entrance of Eridan's hole.

“A-ah, careful, Kar,” Eridan said. He could feel the cool plastic pressing against his ring. With Karkat looming over him, he didn't feel as though he was in as much control of the situation as before. He almost gulped as his whimpering caused Karkat's mouth to twist in a sadistic grin.

“What's the matter, Eridan?” she said. “Reality not living up to the fantasy?”

“No. Actually, maybe, if all you're going to do is fuckin' talk.”

Without any warning, Karkat thrust her hips forward, forcing the head of the strap-on into Eridan's arsehole. He yelped, sudden pain flooding him.

“Hey, fuckin' gently, you stupid nooksucker!”

“Ready for the rest?” Karkat said, almost sweetly.

“Wait, fuck nAAAAGGGGH!”

Karkat slammed the rest of the strap-on home, reaming out Eridan far faster than was comfortable. His screams filled the room. He clenched his hands into tight fists, nails digging into his palms. Tears pooled in his eyes, then overflowed and made black mascara trails roll down his cheeks. His chest felt like it was going to burst as his need to breathe and his desire to scream warred with each other, until at last he was able to take a shuddering gulp of air. That was enough to give him a semblance of control over his body. He feebly tried to throw Karkat off, but every move he made just brought more pain, so in the end he just lay still and waited for it to be over.

When the pain had subsided from unbearable to merely feeling like his arse was on fire, Eridan blinked the tears out of his eyes and said, in between sniffles and sobs, “Don't you ever – ahuh – don't ever do that again.”

“Trust me,” Karkat said sourly, “I won't give myself the opportunity.” Then she smiled and purred, “Besides, I thought this was what you wanted?”

“Not like this, you fuckin' -” His insult was cut short as Karkat reached out and slapped him hard. He clutched at his cheek and gaped at her. “You dare-”

She slapped him again. “Yeah I dare. Because I know you love it, don't you?” Another slap. Eridan whined. “And you know, I'm beginning to enjoy it a little too.” That was true enough. The feeling of dominance fizzled in her blood, all the old trollish instincts coming to the fore. They screamed their demands to take, to use, to control. Karkat looked down at Eridan's tear and make-up streaked face, at the purple bruises forming where her palm had met his skin, and at the impotent anger in his expression. “You know,” she said, “you're looking pretty pitiable right now.”

Eridan choked down his shock at those words. He couldn't ever have imagined Karkat of all people becoming matesprits with him. Besides, he couldn't possibly reciprocate. Right now she was anything other than an object of pity. She was terrifying.

“Just...do what you're going to do,” he muttered.

Karkat gave no response, but pulled back. The strap-on slowly slipped out. Eridan felt more twinges of pain in the tissues of his abused rectum, but they were mere prickles compared to the agony of before. Karkat pulled out most of the dildo, leaving just the head lodged inside. She grabbed Eridan's legs and practically folded him back on himself. He felt his cock pressing into his stomach. To his amazement, it was still hard, and had even developed a little bead of purple-tinted pre-cum at the very tip.

Karkat either didn't notice or didn't care about Eridan's dick. Probably a combination of both, Eridan reasoned, as she seemed far more intent on flipping the humiliation tables on him as fast as possible. She thrust back in, slower than when she'd first entered him, but still fast enough to make him groan as his arse struggled to accommodate the dong's bulk. She bottomed out, held herself there for a moment, then repeated the cycle. Eridan found it easier to take this time, and behind the pain was something that might be called pleasure.

As Karkat built her momentum, she found that her new body could feel good too. When she forced the strap-on into Eridan's arsehole, she felt it push back against her pussy, the leather of the harness rubbing against her clitoris. She sensed a growing need within herself. It was like having a hard-on, but more...inverted? She wasn't sure how to describe it. Everything felt new and yet familiar at the same time.

And then there was the wetness. Karkat knew perfectly well what was going on, but it was still weird to experience it. Her vagina drooled a steady stream of juice, turning the inside of the harness into a swampy mess that slid deliciously against her folds. Pounding Eridan's arse made her moisture leak out around the edges, carving little runnels down her thighs and dribbling out onto Eridan's buttocks.

Morseo than in her male form, Karkat was aware of her nipples. Maybe it was because they came as part and parcel of the most noticeable changes to her anatomy, or maybe it was because they were just so much bigger and more sensitive than before. Either way, both of the pert nubs stuck out in startling erection, begging for attention almost as vocally as her pussy. 

Karkat let go of one of Eridan's legs – he gratefully let it relax and rest on her shoulder – and brought her hand up to her breasts, squeezing the tender flesh. She flicked an experimental fingertip across one of her nipples and found it produced a burst of pleasure that made her gasp out loud. She played with her tits, focussing on their stiff little summits as much as she possibly could. Her eyes closed as for the first time she truly enjoyed her femininity.

Eridan was beginning to enjoy himself too, now that his arse had become accustomed to the strap-on. Karkat was still giving him a violent fucking, but there was a bit less anger behind it now. He found pleasure in the feeling of tight fullness when Karkat's hips pressed against his butt and forced the dildo into him, sighed as it left and brought both relief from the stretching and a sense of emptiness, then gasped as it reamed him out again. The constant sliding of hard plastic over sensitive nerves produced a continuous buzz, and every so often a nova of almost unbearable pleasure would flare within him as Karkat angled the dildo just right to bump against his prostate. It was all he could do to keep himself from moaning out loud when that happened, but he made the effort. He feared Karkat's scorn, though he didn't really know why.

With all of Eridan's attention focussed on his arsehole, his cock went unattended to. Soon though, it became impossible to ignore. It was a hot, pulsing, solid rock of an organ. His balls felt swollen. They drew down great loads of fluid from his genebladder, ready for the first volley of his climax; subsequently, his cockhead leaked pre-cum, a purple stain spreading out across his dishevelled skirt.

Eridan took hold of his cock and began to run his hand up and down its length, spreading his sticky-slippery pre out along his shaft. It felt incredible; having his prick and his arse stimulated at the same time produced sensations beyond compare to any other debauchery in which he'd indulged. He clapped his hand to his mouth, trying to muffle the little moan of “Oh...oh fuck,” that escaped him. He wasn't going to add to his humiliation if he could help it.

Karkat could hardly fail to notice his hands moving to opposite ends of his body, though, and she gave Eridan a smirk that set his teeth on edge. She took his squeaks as a sign to pound his butt even harder, perhaps trying to spoil his pleasure with a little more pain. It had the opposite effect: the extra speed was just what he needed. He wailed in ecstasy and bucked his hips as best he could against her force. Now the strap-on hit his sweet spot with almost every thrust.

Eridan's hand flopped limply from his mouth as he opened it in a raucous scream. Conversely, the hand he had around his cock gripped it hard as it spouted gout after gout of hot purple seed across his stomach, his chest and, in one particularly vigorous spurt, his face. He shuddered bodily, the contractions of his balls sending surges of sexual delight through him. His prostate, still mercilessly battered by Karkat's unceasing thrusts, felt like a node of pure pleasure, and his arse pulsed around the strap-on as though trying to draw it even deeper within.

Karkat looked down triumphantly as her victim writhed in climax. As his orgasm subsided, she gave Eridan a few more desultory thrusts and said, “Enjoy that, freak?” Eridan could only moan weakly and nod in response.

Karkat pulled her strap-on from Eridan's arse, a little trickle of well-used lube dribbling from his distended hole after it. She sat back and watched Eridan recover, wondering what her next move should be.

Eventually, Eridan sat up and arranged himself into as dignified a pose as he could manage. He grinned and said, “Gotta admit, Kar, you started a bit rougher than I liked, but that was pretty fuckin' good.”

“Yeah, yeah,” Karkat said. It was a magical adventure for everyone. Now you're going to turn me back into a male and we're all going to forget that this happened.”

“Are we?”

“Yes,” said Karkat, with vehemence.

“Well I could do that,” Eridan said, “Or I could give you some of the attention you clearly so desperately need.” He nodded in the general direction of her crotch.

Karkat looked down, and saw that her thighs were completely streaked in the moisture of her pussy. Even the leather of the strap-on was soaked in it. And now that it had been pointed out, her earlier arousal returned like a stick of dynamite glued to a boomerang. Her desire to be penetrated radiated out from her pussy through her whole body. She could feel her swollen cunt lips pressing hard against the strap-on, and felt her clit throbbing with every beat of her heart.

“I...fine,” she said. “But I'm only doing this for me. And I – ahh!”

Karkat's words were cut off as something strange started happening within her groin. Her clitoris felt like it was swelling far beyond its normal capabilities. There was a sensation of pressure that was rapidly growing painful, like her clit was pushing up too hard against the strap-on. She quickly unbuckled the harness and pulled it down her legs. She looked down, and saw that her first impressions had been right. She and Eridan watched, mouths agape as her clitoris grew, pushing out from beneath its hood. It bulged outwards, changing its shape and developing a urethra, although her female version of that remained perfectly intact. Something was going on behind the obscene growth; it felt like new channels were plumbing their way into her genebladder, creating alternate routes for her genetic fluid to flow through.

Her clit stopped growing and stayed still for a moment, making it look like someone had taken a male glans and a tube of glue and stuck the former to the top of her vulva for their own perverse amusement. After a few seconds it grew outwards, a smooth grey shaft developing behind what Karkat was able to think of as the head of her penis. Her greatly stretched clit hood grew behind it, wrapping itself around the new flesh, becoming longer and thicker. As the growth of her cock slowed and then ceased, the skin continued up and around her cockhead, formed a neat hole around the tip and settled into place as her foreskin.

Karkat stood stock still, waiting for any other change. Nothing happened, and she started running her hands around her body, desperately searching for something else to prove her male. There was nothing. She had one cock, sans balls, and all the other usual markers of femininity were still in place.

Eridan dared to speak, “Well err...is that close enough for you?”

Karkat went off like a dropped crate of nitroglycerine. “NO IT IS NOT GOGDAMN CLOSE ENOUGH, ERIDAN. WHAT THE FUCK IS HAPPENING HERE? I GET MY DICK BACK BUT NOTHING ELSE? THIS IS ABSOLUTE HOOFBEASTSHIT. FIX IT. NOW!”

Eridan took a step back. “Whoah, whoah, easy there. It just looks like whatever happened to you wore off partially. I can still make you fully male again. Or you could wait for the rest of you to change. In the meantime...”

“What?”

Eridan's lip curled. “You're pretty hard, and pretty wet, Kar.”

Karkat looked down. Her reformed penis did indeed throb in full erection, and below that her pussy and inner thighs were shiny with her juices. Her rage faded to its normal background level, and her arousal came back to the forefront of her mind. Thoughts of the kind of carnalities she could enjoy with both sets of organs filled her head, and her loins responded appropriately, heat flaring within them.

Eridan was saying something. Karkat cleared her head of her horny musings, and made herself listen. “So how about it? I could turn you back now, or I could give you some attention, like I said."

“Alright. But I stay in control. On your knees.”

Eridan smiled and knelt down. Karkat took two steps towards him and grabbed his hair. He knew what was coming, and opened his mouth wide. Karkat was in no mood for foreplay; her cock was a needy thing after its absence, and it demanded a warm hole to fill right away. She plunged her prick into Eridan's mouth, shuddering as his lips encircled it and his wet tongue slid along its length. She hit the back of his throat and he gagged a little, recoiling reflexively. Karkat tightened her grip on his hair and forced him back down, then relented. Reasoning that she might get a better blowjob if she let him work at his own pace, she loosened her grip, just lightly holding the back of his head to let him know that she was still in charge. He looked up questioningly, her cock still in his mouth. She nodded down at him, and he got the message.

Eridan pulled back, ran his tongue around the tip of Karkat's cock, then slowly sucked it back in, keeping his lips wrapped tight around its bulk. He held it near the back of his mouth for a moment, wriggling his tongue left to right, over and under, then repeated the motion. He started to randomise things a little bit, changing what he did with every stroke. He pressed the tip of his tongue into the bottom of her shaft as he drew it out, gave her head a quick, gentle nip as it passed his teeth, then took it out of his mouth entirely and licked it all over before taking it back in much quicker than before.

Karkat moaned, unable to believe how good Eridan was for someone who'd, she guessed, never actually sucked dick before. She glanced over at the discarded strap-on and wondered if he'd practised on it or something similar before. Whatever the reason, her cock felt like it had died and gone to cock heaven, and had been good enough to take the rest of her along and let her see what it was like to be an extremely satisfied penis. Her snatch was responding too, pulsing along with every bit of pleasure inflicted on her cock and producing yet more of its already copious lube. Karkat put her hand between her legs from behind, gently running a fingertip over her labia. She'd need attention there soon enough.

Eridan's thoughts ran along the same lines. Tasting cock and smelling pussy at the same time was driving him wild. He'd already upped his speed to the point where Karkat's prick was in danger of penetrating his throat, and, unsure of his ability to deepthroat, he was wondering whether there was anything he could do to prevent Karkat from pressing the issue. Taking on her other pleasure centre seemed like a good plan, and to that end he slid his fingers up her thighs to her puffy nether lips. His hand touched hers. She gasped, and jerked it away, making him smile internally. As he continued to suck her cock, he readied two fingers and pushed them deep into her grasping cunt.

Karkat's “Ahh!” was much louder than she liked, but her embarrassment was soon washed away in a tide of delight. Eridan's fingers probed their way into all the right places, seeking out the softest spots and untouched, virgin nerves. Her walls contracted tight around his digits, urging them on. He was happy to oblige, pumping them up and down her hot tunnel with gusto. He developed a clever little reciprocal system: fingers in while her cock was out of his mouth, fingers out while it was in. She didn't go without pleasure of any sort for one second. She closed her eyes and luxuriated in the sensations sweeping through her.

Eridan could see the effect he was having on Karkat. Confident that he'd found the right combination of actions to assure her pleasure, he stopped experimenting, focussing on keeping up his rhythm. It was the wrong approach. Karkat quickly grew bored. Amazing as his lips felt wrapped around her dick, something felt out of balance. Two fingers in her pussy wasn't cutting it any more; she could feel the sexual energy growing in her cock far faster. She decided to do something about it. She tangled her fingers in Eridan's hair and stopped him from moving, pulling her prick free from his mouth. She reached down and took his hand away from her crotch. His fingers slipped out of her, trailing juices.

“Huh? Didn't you want this?” Eridan asked. She angled his head up, thrust out her hips. Her dick flopped against his forehead, dribbling pale red precum into his hair, while she brought his lips into contact with her lower, lewder ones. “Lick,” she demanded.

Eridan changed tack with commendable speed. He turned out to be just as skilled with his mouth when he was mainly licking rather than sucking, and Karkat found herself enjoying herself as much as she had when they'd first begun. Her labia were already spread wide open, puffy and engorged. Eridan ran his tongue around their edges before plunging his tongue deep into her opening, coating his tastebuds in the slightly tangy, slightly sweet flavour of her juices. His tongue thrashed inside Karkat, and she moaned out loud, making herself blush, embarrassed again at what felt like a little surrender. Eridan didn't notice. He was far too intent on ministering to the glorious treasure in front of him to notice what its owner was doing.

With his lips suctioned tightly to the edges of Karkat's hole and his tongue wriggling around inside, Eridan felt like he was frenching her pussy. He wryly considered the fact that he'd never even thought about kissing her in the normal way, and yet here he was with his head shoved between her thighs. He wondered if she might let him steal a kiss when this was all over. Maybe when he'd turned her male again she'd...he'd be grateful enough to allow it. Probably not, though. He cleared the thoughts from his head and refocussed his attention on pleasing her.

Before Karkat could grow bored, Eridan showed some initiative and started something different. He slipped his tongue from her vagina and licked his way up the length of her slit, over the female edition of her urethra (with a little trepidation, but, unused, it tasted no different from the rest of her) and up to the base of her cock. A little theory had occurred to him, and he wanted to see if he was correct. He stiffened his tongue and jabbed the tip of it towards the point where Karkat's penis joined her groin.

His guess was correct. Karkat's scream practically shook the room. Although her clitoris had completely grown out into her cock, the dense little nerve cluster it had contained was still in exactly the same place. Eridan grinned and proceeded to mercilessly exploit his discovery. He went back down to her hole, dipped his tongue in (more moans), dragged it back out and went straight into a slurp that ended with a vigorous licking straight on her sweet spot (more squeals). He finished by licking his way up her shaft, swirling his tongue around her cockhead (gasps were the result this time).

With his new knowledge, Eridan was able to keep Karkat entertained far longer than before. He switched between licking her pussy, sucking her cock and tonguing hard at her ex-clitoral nerves. He was completely intent on pleasuring her until he realised she was saying something.

"Enough," she said. "Enough." She disengaged her genitals from his face and took a step back. She put her hand on his chest and pushed. With a surprised yelp he fell back, catching himself just in time to stop his head from hitting the floor. His skirt rose up, and his cock, neglected since he'd started licking her, sprang out once more fully erect and rock hard with desire. Karkat smiled and licked her lips. She wondered how having something as big as that inside her would feel, given how good just two fingers had been.

With some nervousness, Karkat squatted down over the tip of Eridan's dick, her labia just brushing the edges. Eridan's fingers aside, she'd never experimented with being penetrated, even as a male, and now she had to deal with a totally unknown quantity. Her female parts seemed to be relaxed, wet and ready enough, however, and her newly regrown cock wanted to go along for the ride. So with a deep breath, she let herself drop and impaled herself full length on Eridan's member. 

They uttered simultaneous moans as they conjoined. Eridan couldn't believe that she'd voluntarily chosen to be the receiver. Her silky walls felt incredible wrapped around his cock. Karkat couldn't believe how good it felt to have a cock inside her. The burst of ecstasy it had produced as it had travelled up her tunnel, inexorably stretching out her soft flesh, had been beyond compare. But she needed so much more. She began to bounce, raising her hips up and slamming them back down.

Little squeals escaped Karkat with every move she made. The initial penetration had been good, but having a cock pistoning inside her was so far beyond that. Her pussy gripped Eridan's stiff member in all the right places and guided it to probe her softest spots over and over again. It seemed to know exactly what to do to extract the maximum pleasure from Eridan's prick.

Eridan didn't know how someone who'd had a vagina for less than an hour was so good at using it, nor did he care. His eyes rolled back in his head even as he closed his lids in sheer bliss. Being fucked in the arse and forced to lick pussy-cock were both wonderful things, but there was nothing quite like having some hot little pail-filler ride his dick, even if she had one too. In fact, seeing Karkat's own stiff prick flopping around in front of him made it even better. He reached out and wrapped his fingers around it, carefully jacking it in time to her motions.

Their mutual ecstasy quickly built as they fucked. Their emotions ran wild; pity mingled with hate until they forged something new and indistinguishable. Their every thought was modulated by the all-pervading demands of trollish hormones and pheromones. At times, their mating became more like fighting than sex. Eridan's free hand went to Karkat's breasts, initially giving them a tentative massage, but becoming rougher and rougher until his nails were piercing skin, leaving bruised red crescents in their pitiless wake. Karkat gave him a warning snarl, and when he didn't relent, she put her hands on his chest and dug her own nails in deep, gouging deep purple trails in his flesh. He hissed, and retaliated by squeezing her cock painfully hard. He thought he had the upper hand, but then Karkat grabbed hold of his balls and crushed them between her fingers twice as roughly. She even twisted a little. Eridan screamed and let go of everything he was holding. Karkat sighed in relief and released his testicles.

Castration averted, they fell back on more conventional ways of causing each other pain, clawing, slapping, pinching, biting. Neither of them really knew why; they just knew that they wanted the other to feel pain and pleasure in equal measure. To that end they kept it up, fighting like demons and fucking like animals until eventually exhaustion got the better of them and they collapsed into each other, panting and bleeding. They became oddly tender, sharing kisses and running their hands over each other's bodies, massaging sore spots and cupping the swells of breasts and buttocks.

Their passions grew endlessly until they were doing little more than pure, mindless fucking. Karkat's eyes were glazed as she hammered herself onto Eridan's shaft over and over. Little whimpers and moans escaped her as she fought her way towards orgasm. Eridan grunted and groaned every time she slapped against him, each thrust pushing him closer to the edge. He slowly jerked her cock, loving the feel of it pulsing and twitching beneath his palm, the warm slipperiness of her pre running down across his fingers.

Eridan came first. As he screamed his body tensed and trembled, his hips raised up off the floor. His cock spurted hard, sending a hot gush of cum deep into Karkat's pussy. She yelped as she felt the sticky warmth flood her tunnel. Her genebladder opened up and greedily drank it in, her belly swelling a little to accommodate two loads of genetic fluid. She hoped Eridan's spell could reverse that; she really didn't want to pass a female-sized measure of slurry with just a cock.

More pressingly, Karkat realised that she hadn't came yet. Eridan's cock was rapidly softening within her, and he was no longer thrusting. She grabbed hold of her catatonic partner's hips and rode him as hard as she could, desperately trying to bring herself off on his detumescing shaft. She had been so tantalisingly close. She resolved to make Eridan regret it if he went completely limp before she got her climax. Luckily for him, he stayed hard enough for her to slam against him once, twice, three times, and then stars erupted in front of her eyes. She threw back her head and practically roared in exultation as her fluttering pussy told every other part of her body that it was feeling pretty fucking good, and that they should all feel the same way. Her spasming walls squeezed out a load of Eridan's cum and her juices, spreading out across his lap and soaking his skirt in yet more purplish stains.

As Karkat's rapture faded, she became aware that something wasn't quite right. There was an itch, a desire that needed to be fulfilled. She looked down and saw her cock, still fat and throbbing, still feebly gripped in Eridan's sweaty hand. She looked disdainfully up the length of his body and into his face, which was turned upwards, grinning stupidly at nothing. She essayed a cruel little smile of her own. The solution to her problem was obvious.

Moving like a snake, Karkat took her erection from Eridan's grasp and hoisted herself off his crotch. Miscellaneous fluids poured from her pussy, covering Eridan as she moved her way up his torso to settle on his chest. She grabbed him by the hair, hauled his head upright and slapped him hard. As he opened his mouth to protest, she jammed her cock inside, thrusting to the back of his mouth and then, without any warning, down his throat. He gagged, and tears sprang from his eyes again, adding more mascara trails to his already thoroughly streaked face. 

Karkat rammed her cock into Eridan's mouth over and over, fucking his throat like it was just any other hole for her to use. Eridan concentrated on not choking. As he'd predicted earlier, he wasn't very good at deepthroating, and he certainly wasn't finding it very pleasant. He coughed and drooled every time Karkat left his airway free, letting thick gobbets of saliva dribble out around her prick. He made an effort to get her to cum as quickly as possible, pursing his lips tight around her shaft.

If anything, Eridan's co-operation just made Karkat more vicious. She hung on to Eridan's horns and relentlessly fucked his mouth, revelling in the sensation of Eridan's tongue slurping around her cock and the tightness of his throat. She loved the way that he swallowed involuntarily whenever she pushed past the back of his mouth, tight rings of muscle squeezing hard around her dick. She could feel her long-delayed penile orgasm bubbling up inside her. Moaning like crazy, she jabbed her prick between his puckered lips harder and harder until, with a wail, she came. She held Eridan's head hard against her crotch as she shot hot wads of cum down his protein chute. 

Eridan gulped down the heavy load, feeling it settle into his gut. He gasped for air as Karkat pulled back, trailing the last vestiges of her seed. Her cock slipped out from between his lips, and he coughed, choking up a blob of her red-tinted cum that oozed out over his chin. Wiping his mouth clear and rubbing his abused throat, he rasped, “Jegus, Kar. Are you done?”

“Yes, I'm fucking done,” Karkat replied. “What gave you the clue? The fact I just used your mouth as a bucket, or something else?” She tried to meet his eyes, but found she wasn't quite able to. With her passions spent and the afterglow from her climaxes fading, she felt an odd sense of shame at how quickly she'd surrendered to her lust spreading through her. It was tempered, though, by the memory of how good it had felt.

“So,” Eridan said. “Enjoy it?”

“Fucking...” There was a brief pause, then Karkat continued, “yeah, I guess. You?”

“Oh yeah.”

Silence reigned again, then Eridan said “So, do you want me to...”

“Turn me back?” Karkat said, a little too eagerly. She stood up, grimacing, as she felt her loosened pussy and drooping cock dribble their warm fluids down her leg. Eridan followed her lead, then went off to find his wand.

Eridan returned with his wand, and pointed it at Karkat. She flinched a little. “It won't hurt,” he said scornfully. He cast his spell, and it was a simple one. A shimmering haze of energy enveloped Karkat and began to transform her, cell by cell, DNA strand by DNA strand. Her boobs were the first thing to go, shrinking into her chest until it was as flat as it had ever been. Her nipples shrank too, the areolae becoming smaller and much less puffy.

The magic started its work on her groin. She gasped, and crossed her legs. Her vagina was sealing itself shut from the top down, and it was the weirdest sensation she'd ever experienced. She touched her hand to her crotch just in time to feel her labia merge together, becoming smooth, bare skin. Nothing happened for a moment, then her skin began to bulge, splitting into two bulbous parts. She winced as her nerves plugged themselves into her new flesh. Her rapidly growing balls joined themselves to her cock, plumbed themselves back into her genebladder. They separated out into individual fluid pumps and regrew their scrotum, settling gently into place.

After that, just some minor adjustments to Karkat's body remained. Some parts thickened, others became thinner. The glow faded, Eridan lowered his wand and Karkat, to his immense relief, once again found himself fully and biologically male. He ran his hands up and down himself, checking that everything was in the right place. He caught Eridan looking and stopped, gruffly saying, “About time. Now where are my gogdamn clothes?”

Uncharacteristically, Eridan made himself useful and helped Karkat gather together his clothes. He handed them over and watched him dress in silence. When Karkat was done, he straightened up and said, “Right. Well...I'm going now. Sicko.”

“I ain't stopping you,” Eridan replied. “But feel free to come back.”

“Yeah right!” Karkat paused. “But if it does happen again, I'll need you to do what you just did.”

“What, all of it?”

“Just...shut up! It probably won't even happen again.”

Karkat stalked off to the transportalizer pad. Eridan, standing there in his cum-covered hair and clothes, his panties still around one ankle, watched him go. The transportalizer powered up and zapped Karkat away. Eridan smirked, and wondered if his white science could turn a male into a female. After all, it had worked perfectly well the other way around, with just some help from natural phenomena. Maybe he could try it out on himself some day.

Karkat stepped off the other end of the transportalizer and, despite himself, smiled. He wondered what had set the whole chain of events in motion. Perhaps it was something he ate? He walked off into the depths of the asteroid, vaguely looking for anything that seemed like it might have been responsible. Purely out of curiosity, of course.

**Notes for the Chapter:**

> After a long hiatus, I've returned to the wonderful world of smutty fanfic. Thanks for reading, and please follow me at http://geistygeist.tumblr.com/ I'm hoping to get a lot more done over the next few weeks!


	3. XY

Some time ago, Karkat had sat down in his room and closed his eyes, purely for the purposes of resting them, certainly not to sleep and be cast into one of those terrifying Gods-spun dream bubbles. When he'd opened them an hour later, he'd stood up and found himself feeling...different. A quick glance in a mirror told him what had happened.

His features had softened, his hips had grown and his stomach had become slightly more slender. He was definitely shorter. Even his hair had lengthened. To top it all off, his chest now bore a pair of breasts that were inadequately constrained by his male-design t-shirt. More privately, his pants felt tight around his widened hips, but loose and empty elsewhere. Dreading what he might see, he unbuckled them, slid them down a little way, then pulled his boxer shorts down after them.

He stared in shock. There was no denying it. He was now a she.

Something in the Veil had changed Karkat, and she had a fairly good idea of what or who it might be. She pulled up her shorts and pants, strode into the transportalizer out of her room and stalked through the corridors of the asteroid lab, a once moderately angry boy who was now a steamingly furious girl. Her target was going to rue fucking around with her like this.

***

Eridan Ampora did a little twirl in front of the mirror, smiling as his pleated tartan skirt clung flatteringly to his legs. Black and purple striped stockings and a tight tank-top bearing his symbol completed the ensemble. His hair had been washed clean of its usual styling product, no mean feat given that it was almost entirely waterproof. His locks now hung in a pair of loose bunches. A dab of tyrian purple lipstick made for a final elegant touch.

Eridan could feel his cock hardening. It always did when he looked at himself like this. It wasn't his fault. He just made such a damn attractive girl. He smiled at his reflection, watched it smile back.

His stiffening member was starting to poke out over the waistband of the too-tight lace panties hidden beneath his skirt. It began to tent the folds of the skirt, making it very obvious what kind of a state he was in. So it was understandable that he panicked slightly when he heard the transportalizer to his chambers charging up and teleporting someone in.

Eridan desperately reached up and wrenched at his top, but before he could get anywhere close to changed, Karkat walked in and began to harangue him.

“ERIDAN,” she screamed. “YOU STUPID FUCKASS! IF YOU'RE GOING TO PRACTICE THAT STUPID WHITE SCIENCE SHIT DON'T GET ANY OF IT FUCKING NEAR ME!”

“Huh, me?” Eridan replied, temporarily distracted by Karkat's rage. “I haven't fuckin' done anything, Kar.”

“OH YEAH!? THEN WHY IN THE NAME OF THE CONDESCE'S RANCID FISHY NOOK AM I A FUCKING...wait, what?”

Karkat broke off, and stared at Eridan. Eridan stared back and realised what was different about his team leader.

“What the...” he began.

“...fuck?” Karkat concluded.

“Why are you...”

“No, why are YOU dressed as a girl?” Karkat said before Eridan could finish his question. It made no difference, as Eridan simply riposted:

“Why ARE you a girl?” He smirked. “Nice jugs, by the way.”

Karkat glared wordlessly at him for a moment. Then she stepped forward, belted him hard across the jaw and while he was stunned, grabbed him by the neck and pinned him against the wall.

“You did this to me”, she said.

“I didn't,” Eridan rasped.

“You did. You and that gogdamn wand of yours.”

“I swear Kar, I fuckin' didn't. It must have been some sort of natural effect. But...I think I can turn you back.”

Karkat glared at him for a moment more, then took her hand away. Eridan gasped for breath and reached up to his bruised throat, rubbing it for a second before grinning foolishly at her.

“You've got a good grip for a girl,” he said. “So what do I call you now? Karkatte? Kattie?”

“Stick with Kar if you don't want to swallow your teeth,” Karkat said, cracking her knuckles.

“Okay, okay, whatever.”

They went quiet for a moment, then Karkat said, “Well?”

“Well what?”

“Well are you going to turn me male again, idiot?”

“Mmmm...no.”

“WHAT!?” Karkat roared, stepping forward again. But Eridan defended himself this time, taking her wrists in his hand and holding her vengeful fists away from his face.

“I'll turn you back, Kar, but you gotta do something for me first.” He grinned creepily.

A sudden flash of fear filled Karkat. She shook her hands out of his grip and took a step back. “Oh no...no way.”

“No way?” Eridan's smile grew wider.

“No way am I letting you fuck me, you freak! It wouldn't have happened when I was male and it's not happening now!”

Eridan widened his eyes in mock surprise. “Why Karkat,” he said, “who said anything about me fuckin' you?”

He turned and crossed the room, riffling through a cabinet set against one wall. He returned, carrying something and saying, “I want you to fuck ME.”

Karkat stared at the contraption Eridan held. It was an assembly of black straps and metal buckles, surmounted by a long, thick, rubbery dong. “That's a...” she said.

“Strap-on, yes.”

“And you just happen to have it lying around.”

Eridan nodded. “Yup.”

“In case someone came along to fuck you with it?”

“Mmhmm.” He seemed entirely unembarrassed about revealing this desire. “Was hoping it was gonna be Fef, you know, but you'll do.”

“Yeah, it's still not happening.”

“You do want to be a boy again, don't you?” Eridan teased. “You can either wait until this wears off, which might be never, or we can have one quick fuck, after which I'll zap you with the awesome power of my white science and we'll both be happy. Well, I'll be happy. Don't know about you.”

Karkat thought, unable to believe that she was even considering it. The idea of even getting close to Eridan was disgusting. But she really had no choice. She couldn't let Terezi or Vriska see her like this. Their laughter would probably burst her eardrums. Eventually she said, “One quick fuck.”

“Unless you want more.”

“Ugh, Gog no.”

“Whatever. Are we doing this?”

“Fine, you win,” Karkat groaned.

“Alright. Strip.”

“What? No!” Karkat grimaced in revulsion.

“Full nudity, or this goes nowhere. My science, my rules.”

“Can't I just put the thing on over my pants?” she asked desperately.

“Nope.”

“You're the worst kind of fucking creep, Eridan.”

“Yeah, but I'm the one with the wand. And I bet you want your wand back, huh?”

Karkat heaved an appalled sigh and pulled her shirt off, freeing her magnificent new tits. Eridan leered. “Niiiice,” he drawled. “You make a pretty hot girl, Kar. Pity you're an ugly guy.”

“Fuck you.”

“You will. Now your pants.”

Karkat hadn't thought much about exposing her boobs. It wasn't much different from going bare-chested as a male, even if Eridan was getting his sick little thrill out of it. But that demand gave her pause for thought. If she took off her pants, she'd only be a pair of boxer shorts away from being completely naked. Reluctantly, she squatted down and took off her shoes and socks, then stood up, popped the fastener of her pants and gripped the waistband. She slowly wriggled them down over her hips, then down to her ankles, where she stepped out of them. Eridan watched with a lascivious glint in his eye. “Now,” he said huskily, his voice almost catching, “your shorts.”

Desperately trying not to blush, Karkat slid off her underpants. When her privates were exposed, she covered them with her outstretched palm, using her other hand to help pull her boxers all the way off. She straightened up and stared defiantly at Eridan.

He tapped his foot impatiently. “Show me,” he said.

Karkat made a face and took her hand away from her crotch, letting Eridan's greedy gaze fall on her delicate, virgin folds. Eridan could feel his cock pulsing harder the longer he looked. He wondered whether he should be the one penetrating, imagining Karkat's warm, unwilling vagina wrapped tight around his prick. He decided against it. Karkat would probably be far from amenable. Besides, he was fulfilling a fantasy here.

“Getting a good look, perv?” Karkat said. Eridan realised he'd been staring at her snatch for a little too long. In lieu of a response, he tossed her the strap-on. She just about caught it, suppressing her distaste for it long enough to hook her fingers around one of the straps.

“Put it on,” Eridan demanded.

Karkat did so, stepping into it and drawing the harness up to her thighs. It fastened snugly around her hips and arse. To her relief, it covered her crotch. Calling it clothing was a bit of a stretch, but at least she wasn't completely naked now.

Eridan nodded approvingly, then went back over to the cabinet from which he'd taken the strap-on. He reached in, grabbed a bottle of lube and brought it back to Karkat. “Oil it up, Kar,” he said.

With a growl, Karkat opened and upended the bottle, squeezed a tiny amount of lube over her prosthetic cock and gave it a cursory rub. Eridan noticed, and gestured for her to put more on. “Nice and thick,” he said, leering. “Do it like you were jacking off your own bulge.”

“You stupid fuckhead,” Karkat said, but she complied. She drizzled the dong in lube and pistoned her clenched hand up and down its length.

Smiling, Eridan imagined the glistening plastic prick filling him. His cock responded to his thoughts, straining hard against the confines of his panties. He reached beneath his skirt and loosened them, letting them drop. He daintily pulled one foot free, keeping them wrapped around the other. He sat down and lay back. His skirt fell back with him; his cock sprang free, standing out proudly from his crotch. He clutched his buttocks and spread them wide apart. Breathing heavily he said, “Alright Kar. Fuck me!”

“Oh, my pleasure,” Karkat snarled. She dropped to her knees and shuffled forwards. She grabbed one of Eridan's ankles and pushed it back, further exposing what Karkat had to admit was a rather nice tight arse. She guided the tip of the slippery dildo to the entrance of Eridan's hole.

“A-ah, careful, Kar,” Eridan said. He could feel the cool plastic pressing against his ring. With Karkat looming over him, he didn't feel as though he was in as much control of the situation as before. He almost gulped as his whimpering caused Karkat's mouth to twist in a sadistic grin.

“What's the matter, Eridan?” she said. “Reality not living up to the fantasy?”

“No. Actually, maybe, if all you're going to do is fuckin' talk.”

Without any warning, Karkat thrust her hips forward, forcing the head of the strap-on into Eridan's arsehole. He yelped, sudden pain flooding him.

“Hey, fuckin' gently, you stupid nooksucker!”

“Ready for the rest?” Karkat said, almost sweetly.

“Wait, fuck nAAAAGGGGH!”

Karkat slammed the rest of the strap-on home, reaming out Eridan far faster than was comfortable. His screams filled the room. He clenched his hands into tight fists, nails digging into his palms. Tears pooled in his eyes, then overflowed and made black mascara trails roll down his cheeks. His chest felt like it was going to burst as his need to breathe and his desire to scream warred with each other, until at last he was able to take a shuddering gulp of air. That was enough to give him a semblance of control over his body. He feebly tried to throw Karkat off, but every move he made just brought more pain, so in the end he just lay still and waited for it to be over.

When the pain had subsided from unbearable to merely feeling like his arse was on fire, Eridan blinked the tears out of his eyes and said, in between sniffles and sobs, “Don't you ever – ahuh – don't ever do that again.”

“Trust me,” Karkat said sourly, “I won't give myself the opportunity.” Then she smiled and purred, “Besides, I thought this was what you wanted?”

“Not like this, you fuckin' -” His insult was cut short as Karkat reached out and slapped him hard. He clutched at his cheek and gaped at her. “You dare-”

She slapped him again. “Yeah I dare. Because I know you love it, don't you?” Another slap. Eridan whined. “And you know, I'm beginning to enjoy it a little too.” That was true enough. The feeling of dominance fizzled in her blood, all the old trollish instincts coming to the fore. They screamed their demands to take, to use, to control. Karkat looked down at Eridan's tear and make-up streaked face, at the purple bruises forming where her palm had met his skin, and at the impotent anger in his expression. “You know,” she said, “you're looking pretty pitiable right now.”

Eridan choked down his shock at those words. He couldn't ever have imagined Karkat of all people becoming matesprits with him. Besides, he couldn't possibly reciprocate. Right now she was anything other than an object of pity. She was terrifying.

“Just...do what you're going to do,” he muttered.

Karkat gave no response, but pulled back. The strap-on slowly slipped out. Eridan felt more twinges of pain in the tissues of his abused rectum, but they were mere prickles compared to the agony of before. Karkat pulled out most of the dildo, leaving just the head lodged inside. She grabbed Eridan's legs and practically folded him back on himself. He felt his cock pressing into his stomach. To his amazement, it was still hard, and had even developed a little bead of purple-tinted pre-cum at the very tip.

Karkat either didn't notice or didn't care about Eridan's dick. Probably a combination of both, Eridan reasoned, as she seemed far more intent on flipping the humiliation tables on him as fast as possible. She thrust back in, slower than when she'd first entered him, but still fast enough to make him groan as his arse struggled to accommodate the dong's bulk. She bottomed out, held herself there for a moment, then repeated the cycle. Eridan found it easier to take this time, and behind the pain was something that might be called pleasure.

As Karkat built her momentum, she found that her new body could feel good too. When she forced the strap-on into Eridan's arsehole, she felt it push back against her pussy, the leather of the harness rubbing against her clitoris. She sensed a growing need within herself. It was like having a hard-on, but more...inverted? She wasn't sure how to describe it. Everything felt new and yet familiar at the same time.

And then there was the wetness. Karkat knew perfectly well what was going on, but it was still weird to experience it. Her vagina drooled a steady stream of juice, turning the inside of the harness into a swampy mess that slid deliciously against her folds. Pounding Eridan's arse made her moisture leak out around the edges, carving little runnels down her thighs and dribbling out onto Eridan's buttocks.

Morseo than in her male form, Karkat was aware of her nipples. Maybe it was because they came as part and parcel of the most noticeable changes to her anatomy, or maybe it was because they were just so much bigger and more sensitive than before. Either way, both of the pert nubs stuck out in startling erection, begging for attention almost as vocally as her pussy. 

Karkat let go of one of Eridan's legs – he gratefully let it relax and rest on her shoulder – and brought her hand up to her breasts, squeezing the tender flesh. She flicked an experimental fingertip across one of her nipples and found it produced a burst of pleasure that made her gasp out loud. She played with her tits, focussing on their stiff little summits as much as she possibly could. Her eyes closed as for the first time she truly enjoyed her femininity.

Eridan was beginning to enjoy himself too, now that his arse had become accustomed to the strap-on. Karkat was still giving him a violent fucking, but there was a bit less anger behind it now. He found pleasure in the feeling of tight fullness when Karkat's hips pressed against his butt and forced the dildo into him, sighed as it left and brought both relief from the stretching and a sense of emptiness, then gasped as it reamed him out again. The constant sliding of hard plastic over sensitive nerves produced a continuous buzz, and every so often a nova of almost unbearable pleasure would flare within him as Karkat angled the dildo just right to bump against his prostate. It was all he could do to keep himself from moaning out loud when that happened, but he made the effort. He feared Karkat's scorn, though he didn't really know why.

With all of Eridan's attention focussed on his arsehole, his cock went unattended to. Soon though, it became impossible to ignore. It was a hot, pulsing, solid rock of an organ. His balls felt swollen. They drew down great loads of fluid from his genebladder, ready for the first volley of his climax; subsequently, his cockhead leaked pre-cum, a purple stain spreading out across his dishevelled skirt.

Eridan took hold of his cock and began to run his hand up and down its length, spreading his sticky-slippery pre out along his shaft. It felt incredible; having his prick and his arse stimulated at the same time produced sensations beyond compare to any other debauchery in which he'd indulged. He clapped his hand to his mouth, trying to muffle the little moan of “Oh...oh fuck,” that escaped him. He wasn't going to add to his humiliation if he could help it.

Karkat could hardly fail to notice his hands moving to opposite ends of his body, though, and she gave Eridan a smirk that set his teeth on edge. She took his squeaks as a sign to pound his butt even harder, perhaps trying to spoil his pleasure with a little more pain. It had the opposite effect: the extra speed was just what he needed. He wailed in ecstasy and bucked his hips as best he could against her force. Now the strap-on hit his sweet spot with almost every thrust.

Eridan's hand flopped limply from his mouth as he opened it in a raucous scream. Conversely, the hand he had around his cock gripped it hard as it spouted gout after gout of hot purple seed across his stomach, his chest and, in one particularly vigorous spurt, his face. He shuddered bodily, the contractions of his balls sending surges of sexual delight through him. His prostate, still mercilessly battered by Karkat's unceasing thrusts, felt like a node of pure pleasure, and his arse pulsed around the strap-on as though trying to draw it even deeper within.

Karkat looked down triumphantly as her victim writhed in climax. As his orgasm subsided, she gave Eridan a few more desultory thrusts and said, “Enjoy that, freak?” Eridan could only moan weakly and nod in response.

Karkat pulled her strap-on from Eridan's arse, a little trickle of well-used lube dribbling from his distended hole after it. She sat back and watched Eridan recover, wondering what her next move should be.

Eventually, Eridan sat up and arranged himself into as dignified a pose as he could manage. He grinned and said, “Gotta admit, Kar, you started a bit rougher than I liked, but that was pretty fuckin' good.”

“Yeah, yeah,” Karkat said. It was a magical adventure for everyone. Now you're going to turn me back into a male and we're all going to forget that this happened.”

“Are we?”

“Yes,” said Karkat, with vehemence.

“Well I could do that,” Eridan said, “Or I could give you some of the attention you clearly so desperately need.” He nodded in the general direction of her crotch.

Karkat looked down, and saw that her thighs were completely streaked in the moisture of her pussy. Even the leather of the strap-on was soaked in it. And now that it had been pointed out, her earlier arousal returned like a stick of dynamite glued to a boomerang. Her desire to be penetrated radiated out from her pussy through her whole body. She could feel her swollen cunt lips pressing hard against the strap-on, and felt her clit throbbing with every beat of her heart.

“I...fine,” she said. “But I'm only doing this for me. And I – aaah!”

Karkat's words were cut off as something strange started happening within her groin. Her vagina felt like it was sealing itself up from the top down. Her clit and labia were swelling far beyond their normal capabilities. There was a sensation of pressure that was rapidly growing painful, like they were pushing up too hard against the strap-on. She unbuckled the harness and pulled it down her legs. She looked down, and saw that her first impressions had been right. She and Eridan watched, mouths agape as her clitoris grew, pushing out from beneath its hood. It bulged outwards, changing its shape and developing a urethra, becoming a cock again. Below, her labia were merging together, becoming a scrotum, bulging out to incubate the developing fluid pumps that were her balls. She could feel something happening internally, new channels plumbing their way up to her genebladder. The last few changes fell into place, and Karkat once again found himself with fully male genitalia.

Karkat looked up at Eridan, who was staring at Karkat's chest. Karkat looked down again, and noticed the conspicuous absence of his breasts. He'd been so focussed on the changes to his crotch that he hadn't noticed the rest of his body changing. Parts had thickened, other bits had become more slender. Everything seemed to be in place; he felt exactly as he had before he'd changed. “Did you do that,” he asked Eridan, suspicion in his voice.

Eridan shook his head. “Not me. I was kinda looking forward to you staying female.”

“Huh. Then I guess it wasn't you who made me a girl in the first place.”

“That's what I told you, Kar.”

“Whatever. I've got no reason to stay here now. Find me my clothes.”

“Wait!” Eridan cried.

Karkat grimaced. “What. Now,” he said through gritted teeth.

“Weeeelllll...can't help but notice that you're pretty hard.”

Karkat looked down. His reformed penis did indeed throb in full erection, and his balls felt tight and engorged, ready to pump out some fluids at a moments notice. Apparently his body didn't care much whether he was male or female, it just knew that it was horny. Thoughts of testing that everything still worked filled Karkat's head, and his loins responded appropriately, heat flaring within them.

Eridan was saying something. Karkat cleared his head and forced himself to listen. “So how about it? You can just go now, or I can give you some attention like I said.”

“Alright. But I stay in control. On your knees.”

Eridan smiled and knelt down. Karkat took two steps towards him and grabbed his hair. He knew what was coming, and opened his mouth wide. Karkat was in no mood for foreplay; his cock was a needy thing after its absence, and it demanded a warm hole to fill right away. He plunged his prick into Eridan's mouth, shuddering as his lips encircled it and his wet tongue slid along its length. Karkat hit the back of Eridan's throat and he gagged a little, reflexively recoiling as Karkat's balls flopped against his chin. Karkat tightened his grip on Eridan's hair and forced him back down, then relented. Reasoning that he might get a better blowjob if he let Eridan work at his own pace, Karkat loosened his grip, just lightly holding the back of Eridan's head to let him know that he was still in charge. Eridan looked up questioningly, Karkat's cock still in his mouth. Karkat nodded down at him, and he got the message.

Eridan pulled back, ran his tongue around the tip of Karkat's cock, then slowly sucked it back in, keeping his lips wrapped tight around its bulk. He held it near the back of his mouth for a moment, wriggling his tongue left to right, over and under, then repeated the motion. He started to randomise things a little bit, changing what he did every stroke. He pressed the tip of his tongue into the bottom of Karkat's shaft as he drew it out, gave the head a quick, gentle nip as it passed his teeth, then took it out of his mouth entirely and licked it all over before taking it back in much quicker than before.

Karkat moaned, unable to believe how good Eridan was for someone who'd, he guessed, never actually sucked dick before. He glanced over at the discarded strap-on and wondered if Eridan had practiced on it or something similar before. Whatever the reason, his cock felt like it had died and gone to cock heaven, and it had been good enough to take the rest of him along to let him see what it was like to be an extremely satisfied penis. His balls were responding too, pulsing along with every bit of pleasure inflicted on his cock and swelling slightly as they drew down yet more fluid from his genebladder. Karkat put his hand between his legs from behind, gently massaging his heavy bollocks. He'd need attention there soon enough.

Eridan's thoughts ran along the same lines. The salty, sweaty taste of Karkat's cock was driving him wild. He'd already upped his speed to the point where Karkat's prick was in danger of penetrating his throat, and, unsure of his ability to deepthroat, he was wondering whether there was anything he could do to prevent Karkat from pressing the issue. Pleasuring other parts of him seemed like a good start, and to that end he slid his fingers up Karkat's thighs, which were still slippery with the juices produced by his vanished pussy. Eridan's hand touched Karkat's. Karkat gasped, and jerked it away, making Eridan smile internally. As he continued to suck Karkat's cock, he palmed his partner's balls and gently closed his fingers around them.

Karkat's “Ahh!” was much louder than he liked, but his embarrassment was soon washed away in a tide of delight. Eridan was massaging Karkat's balls just right. His fingers contracted and relaxed so delicately, fingertips probing into the softest, most sensitive spots. He pressed his index finger up between them, separating them out and squeezing each one individually. He let them go, slid his fingers behind them and rubbed Karkat's perineum. It was slick with sweat, and Eridan felt Karkat's cock jump in his mouth when he pushed his fingertips hard against it. Karkat's balls pulsed hotly, urging Eridan on. He was happy to oblige, teasing Karkat's testes with great gusto. He relaxed his assault on Karkat's cock, slipping it out of his mouth and just sucking at the tip, but Karkat didn't go without pleasure of any sort for one second. He closed his eyes and luxuriated in the sensations sweeping through him.

Eridan could see the effect he was having on Karkat. Confident that he'd found the right combination of actions to assure Karkat's pleasure, he stopped experimenting, focussing on keeping up his rhythm. It was the wrong approach; Karkat quickly grew bored. Amazing as Eridan's lips and fingers felt wrapped around his dick and balls, he needed more. Even combined, oral and digital pleasure weren't cutting it any more; he could feel the desire growing in his cock far faster than Eridan could sate it. Karkat decided to do something about it. He tangled his fingers in Eridan's hair and stopped him from moving, pulling his prick free from Eridan's mouth. He reached down with his other hand and took Eridan's away from his crotch. Eridan let go of Karkat's balls and looked up, saying “Huh? Don't you want this?”

“Time for something different,” Karkat responded, his voice heavy with desire. He gripped one of Eridan's horns and hauled him up. Eridan was spun around and prodded over to a desk at the edge of the room. To Eridan's weak protests, Karkat swept it clear of various detritus and made Eridan bend over it, a firm hand pressing him down in a way that told him to stay there. Karkat moved away for a moment and Eridan risked a peek over his shoulder. He saw Karkat pick up the bottle of lube with which he'd made him anoint the strap-on. Now Karkat used it on his flesh-and-blood cock with a lot more enthusiasm, liberally coating his prick in the cool liquid. He moaned as he used both hands to work it into his shaft, and Eridan had to stifle the beginnings of a giggle. Karkat's head whipped round to glare at him, and he just as quickly turned back to the wall. 

When Karkat had thoroughly lubricated his cock, he dropped the much depleted bottle and went back to Eridan. Eridan felt Karkat (and how much bigger his hands were now he was a male again!) squeeze his buttocks through his skirt, then they flipped up the flimsy garment, putting his hindquarters on full display.

Karkat couldn't help but admire the wonderful vista of arse spread out beneath him. Eridan's butt was taut and muscular, free of the insulating layer of fat possessed by the deeper seadwellers. His balls and startlingly erect cock hung below, between his parted thighs. Eridan gasped as Karkat reached down and spread his cheeks, fingers kneading bare flesh this time. The action revealed Eridan's arsehole, which was still slightly open and glistening enticingly. Karkat rubbed Eridan's butt harder, his thumbs coming close to that tight little pucker. He ran a thumb around its edges, making Eridan whimper in anticipation.

“You like that, bitch?” Karkat asked. He slipped the tip of his thumb into Eridan's hole. Eridan groaned, and his sphincter reflexively tightened around Karkat's thumb. Karkat pushed it in further, past the first knuckle, then up to the second, wriggling it around inside. Eridan moaned and pushed his arse back against Karkat's hand, begging for more.

Karkat withdrew his thumb and took hold of his cock. He pushed it up between Eridan's buttocks and thrust a couple of times. His oiled shaft slipped along Eridan's crack like they were made for each other. He gripped Eridan's cheeks and pressed them tight around his prick. The softness of Eridan's skin coupled with the hardness of his muscles felt amazing wrapped around his penis. Karkat bucked his hips, sliding his cock up its fleshy enclosure. As Karkat did so, Eridan murmured pleasurably. He hadn't thought he'd get anything out of Karkat using him like this, but the underside of Karkat's prick was pressed hard against Eridan's arsehole, building up a tantalising warmth as it rubbed against his opening.

Karkat could easily have hotdogged Eridan's butt until he came, but his cock demanded more tightness, more heat. He unwrapped Eridan's buttocks from around his prick and spread them open once more. He stepped back a little and positioned his cockhead against the entrance to Eridan's hole. The desire to make Eridan scream as he had with the strap-on came upon him, but he had the comfort of his actual dick to think about this time. So slowly and carefully, he began to penetrate his partner, feeling the edges of Eridan's arsehole gradually envelop his penis. Eridan moaned as he felt himself delightfully stretched around Karkat's invading member. He stuck a finger on his mouth and bit down on it as he tried to relax, his sharp teeth prickling his skin.

Karkat worked the entirety of his glans into Eridan. Inside he was tight, but still slippery with leftover lube. Coupled with the stuff coating Karkat's cock, it was very easy to move. Karkat could wait no longer, and emboldened by this new knowledge, he thrust himself full-length into Eridan's arsehole. Eridan yelped and bit down a little too hard on his finger, pain assailing him from both ends of his body. But both agonies faded after just a few seconds, and the one in his arse left him full of a heat that made him beg Karkat for more.

Karkat waited for Eridan's walls to settle comfortably around his cock, feeling them twitching and tightening as though unsure whether to accept him in or push him out. When all was still, he obliged Eridan, pulling out, and then, before Eridan's walls could tighten up again, he thrust back in slowly but firmly. There was no pain for Eridan this time. He moaned; Karkat's wonderful prick touched all the right nerves, pressed into his prostate just right.

Moaning himself at the amazing sensations flowing from his cock, Karkat fucked Eridan faster and faster. The silky feeling of Eridan's lubed walls felt amazing. His balls slapped up against Eridan's arse with every thrust he made, the impacts sending little shocks of pleasure racing through him. He could feel the rings of muscle in Eridan's rectum rippling around his shaft, squeezing it in a way that suggested they knew exactly how to extract the maximum amount of pleasure from it.

Eridan was glad that Karkat's brush with femininity hadn't robbed him of his experience with male genitalia. Being fucked with a strap-on and forced to suck cock were both wonderful things, but there was nothing quite like having some hot little pail-filler fuck him with a big, hard, living dick. He reached back and gripped one of Karkat's buttocks, trying to make Karkat do him harder and faster.

Their mutual ecstasy quickly built as they fucked. Their emotions ran wild; pity mingled with hate until they forged something new and indistinguishable. Their every thought was modulated by the all-pervading demands of trollish hormones and pheromones. At times their mating became more like fighting than sex. Eridan kept his hand on Karkat's arse and reached out with his other one to Karkat's side. At first he gave them both a tentative massage, but became rougher and rougher until his nails were piercing skin, leaving bruised red crescents in their pitiless wake. Karkat gave a warning snarl, and when Eridan didn't relent, he bent his body over him and bit his shoulder. Eridan hissed, twisted under Karkat's weight, brought his hand up and raked his nails down the side of Karkat's face, bloodying his partner's ear. He hooked his nails in, squeezing and pulling, threatening to tear flesh. Karkat screamed and put his hand between Eridan's legs, fumbling around for his target. His fingers fell upon Eridan's balls and he grabbed hold of them, squeezing them just to the point before serious injury. At the same time he slammed his hips into Eridan, the sudden burst of rough speed turning his cock into an instrument of pain. Now it was Eridan's turn to scream, and he let go of everything he was holding. Karkat sighed in relief and released Eridan's testicles, prompting a similar sigh of relief from him.

Castration and mutilation averted, they fell back on more conventional ways of causing each other pain, clawing, slapping, pinching, biting. Karkat's dominant position gave him the advantage, but Eridan tried to give back as good as he got. Neither of them really knew why they were doing it; they just knew that they wanted the other to feel pain and pleasure in equal measure. To that end they kept it up, fighting like demons and fucking like animals until eventually exhaustion got the better of them and they collapsed, Eridan onto the table and Karkat, panting, onto Eridan's back. They became oddly tender. Karkat kissed the nape of Eridan's neck and reached down to stroke his partner's cock. Eridan squirmed and moaned. He caressed Karkat's sides, reaching up with one hand to rub Karkat's back and down with another to cup the swell of his buttocks.

Their passions grew endlessly until they were doing little more than pure, mindless fucking. Karkat's eyes were glazed as he hammered himself into Eridan's arse over and over again. He rhythmically jerked Eridan's cock, loving the feel of it twitching hotly beneath his palm, the slipperiness of Eridan's pre running down across his fingers. Little whimpers and moans escaped him as he fought his way to orgasm.

Eridan's head was down on the table, his mouth open and drooling. He grunted and groaned every time Karkat slapped against him, every thrust pushing against his sweet spot, sparking notes of joy throughout each knotted little nerve cluster. His cock felt like a solid rod of pleasure. The motions of Karkat's hand brought the heat up another notch, brought him closer to the edge. He could feel ecstasy rushing into his every cell, bringing a kind of fuzziness to the edges of his brain. He slowly raised his head, each thrust of Karkat's knocking a short gasp out of him. His eyes fixed on the wall, he took a deep breath.

With a scream, Eridan came. His cock spurted gouts of cum, splattering a puddle of his purple fluids across the floor below. He shook as a dual wave of pleasure from his prick and his prostate ravaged their way up his body. His back arched, a bolt of lightning flashed through his mind and then with a satisfied sigh he slumped down onto the table, closing his eyes and riding out the aftershocks as Karkat continued to pound his arse and rub his dripping prick.

Karkat knew that he was almost there himself. He thrust his cock into Eridan with a speed that made his muscles ache and his breath run short. His partner's exhausted inner walls feebly milked his cock, urging on Karkat's long-delayed orgasm. Karkat slowed, gathering his strength, then unleashed a barrage of thrusts. He was still fucking when he came, his climax taking him in a flash. The pleasure mingled with his tiredness and he fell across Eridan's back as he shot his load deep inside. Eridan moaned weakly, feeling a bladder's-worth of hot genefluid rush into his rectum. Karkat filled Eridan so full that the red-tinted cum leaked out around Karkat's drooping cock, dribbling into and mingling with the purple lake below. Karkat pulled his prick from Eridan's arsehole, another torrent of his seed rushing out from the stretched hole.

Karkat lay clutching Eridan's shoulders. His trembling legs could barely hold him up, so blasted by pleasure and overworked from fucking they were. Karkat and Eridan stayed where they were for a minute or two, savouring the post-coital closeness that they knew could not last long. They both gasped for air, feeling their sweat and cum dry into stickiness. Eventually, Eridan stirred and spoke:

“I...” he panted. “I should have just turned you back into a guy from the beginning.”

“Yeah, you should,” Karkat said. “But then I guess we wouldn't have done this.”

Eridan smirked. “Oh, so I turned you around? I was good, huh?”

“Keep your fucking ego in check, shithorns,” Karkat growled. “You were just a hole. I did all the work.”

“Pretty good hole though, right?”

“Maybe,” Karkat grudgingly admitted. He peeled himself away from Eridan and stood up unsteadily.

“Where're you going?” Eridan asked.

“To find a wet cloth. I look like the insides of an empty bucket.”

Uncharacteristically, Eridan made himself useful while Karkat was snooping around and gathered together Karkat's clothes. When Karkat had cleaned himself as best he could, Eridan handed them over and watched him dress in silence. When Karkat was done, he straightened up and said, “Right. Well...I'm going now. Sicko.”

“I ain't stopping you,” Eridan replied. “But feel free to come back.”

“Yeah right!” Karkat paused. “But if it does happen again, I want you ready to turn me back into a male.”

“And then?”

“Just...shut up! It probably won't even happen again.”

Karkat stalked off to the transportalizer pad. Eridan, standing there in his cum-covered clothes, his panties still around one ankle, watched him go. The transportalizer powered up and zapped Karkat away. Eridan smirked, and wondered if his white science could turn a male into a female. After all, something had done it in reverse before his very eyes. Maybe he could try it out on himself some day. Being able to switch sex at will would be quite useful, and definitely very fun.

Karkat stepped off the other end of the transportalizer and, despite himself, smiled. He wondered what had set the whole chain of events in motion. Perhaps it was something he ate? He walked off into the depths of the asteroid, vaguely looking for anything that seemed like it might have been responsible. Purely out of curiosity, of course.

**Notes for the Chapter:**

> After a long hiatus, I've returned to the wonderful world of smutty fanfic. Thanks for reading, and please follow me at http://geistygeist.tumblr.com/ I'm hoping to get a lot more done over the next few weeks!

**Author's Note:**

> After a long hiatus, I've returned to the wonderful world of smutty fanfic. Thanks for reading, and please follow me at http://geistygeist.tumblr.com/ I'm hoping to get a lot more done over the next few weeks!


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